1. Field of the Invention
This invention relates to engine aftertreatment systems and more particularly relates to apparatus, systems and methods for real-time diagnosis of a NOx-adsorption catalyst.
2. Description of the Related Art
Environmental regulations on internal combustion engines have become steadily more stringent in recent years. The use of aftertreatment systems to reduce engine emissions has become an important part of the emissions package for many engines. One important category of aftertreatment systems is the NOx-adsorption catalyst (NAC). In one typical design, these catalysts adsorb NOx compounds and oxygen while an engine runs lean, and desorb and reduce the NOx compounds in a regeneration cycle while the engine runs rich.
The catalytic materials in the NAC age over time and become less effective. Specifically, the NAC will lose capacity to store NOx compounds and oxygen, thereby requiring more frequent regenerations and increased emissions. There is currently no direct measurement of the NAC NOx compounds and oxygen storage capacity. A determination that the storage capacity for these compounds has degraded enables a myriad of mitigating responses to a degraded NAC. For example, engine controls can respond with increased regeneration frequency, a service lamp can be engaged, or an emissions control scheme within the engine can be invoked.
Further, regulations require an On-Board Diagnostic (OBD) plan in many applications, and a method to detect degradation of the catalyst element of a NAC meets the requirements of these regulations. The diagnostics to meet OBD regulations should run with an engine as the engine is used (i.e. in real-time) and not require special stops or testing activities to be effective.
From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method for real-time diagnosis of a NAC. Beneficially, such an apparatus, system, and method, would enable diagnosing the NAC using commonly available sensors, and not require excessive computer power.